The maximum concentration of gas achievable in a liquid is governed by Henry's Law. The relatively low solubility at ambient pressure of many gases (for example, oxygen or nitrogen) within a liquid such as water results in a low concentration of the gas in the liquid when these are mixed. There are, however, many applications where it would be advantageous to employ a gas in a liquid mixture where the concentration of the gas within the liquid greatly exceeds its solubility at ambient pressure.
High-pressure compression of a liquid within a liquid emulsion or solid within a liquid suspension can be used to achieve a higher dissolved gas concentration, but disturbance of this gas supersaturated liquid through ejection into a 1 bar environment from the high pressure reservoir will generally result in cavitation inception at or near the exit port. The rapid evolution of bubbles produced at the exit port vents much of the gas from the liquid, so that the high degree of gas concentration within the liquid is considerably reduced at the ambient pressures outside the high pressure vessel. Additionally, the presence of bubbles in the effluent generates turbulence and impedes the flow of the effluent beyond the exit port.
A wide variety of applications would benefit from ejection of a gas-supersaturated fluid from a high pressure reservoir into an ambient pressure environment in a manner which does not involve cavitation inception at or near the exit port. For example, organic material and plant waste streams--e.g., paper mills and chemical plants--often require an increase in dissolved oxygen content before these streams can be safely discharged into a body of water. U.S. Pat. No. 4,965,022 recognizes that a similar need may also occur at municipal waste treatment plants and that fish farms require increased dissolved oxygen levels to satisfy the needs of high density aquaculture. Other applications are disclosed in U.S. Pat. No. 5,261,875.
There are many prior art references which disclose methods of enriching the oxygen content of water. For example, U.S. Pat. No. 4,664,680 discloses several conventional types of apparatus that can be used for continuously contacting liquid and oxygen-containing gas streams to effect oxygen absorption within the liquid. Specifically, pressurizable confined flow passageways are used to avoid premature liberation of the dissolved oxygen before it is incorporated within the fluid. Other oxygen saturation devices are disclosed in U.S. Pat. Nos. 4,874,509 and 4,973,558. However, these techniques leave unsolved the problem of how to eject the gas-enriched fluid solutions from a high pressure reservoir into a lower pressure environment without the formation of bubbles in the effluent at or near the exit port.
In a previous application, Ser. No. 08/581,019, filed Jan. 3, 1996, I describe a method for ejection of gas-supersaturated liquids from a high pressure to a low pressure environment without cavitation, consisting of extrusion of the fluid through capillary channels and compression to remove cavitation nuclei along the inner surface of the channels. Hydrostatic compression at pressures between 0.5 kbar and 1.0 kbar rapidly removes cavitation nuclei and bubbles from the liquid. When a gas source is used to both pressurize the liquid and achieve a desired concentration of a relatively insoluble gas in the liquid, it is generally necessary to maintain the gas pressure in the 10 bar to 150 bar range.
The complete absence of cavitation inception in water saturated with oxygen at high concentrations permits its in vivo infusion into either venous or arterial blood for the purpose of increasing the oxygen concentration of the blood while avoiding the formation of bubbles which tend to occlude capillaries.
In contrast to this capillary channel technique, the present invention dispenses with the necessity of compressing fluids within capillary channels, relying instead on use of gas-supersaturated emulsions and suspensions.